KR100688329B1 - Spread spectrum system communication unit and its method for establishing high speed synchronization - Google Patents

Abstract

It is possible to establish high-speed synchronization even in a state where the frequency and phase of the carrier wave are not strictly known on the receiving side.

As a spread spectrum communication device having a toggle detector 101 and a demodulator 105, the toggle detector 101 detects a candidate of a toggle point existing in a received signal carrier, and the demodulator 105 The received signal is demodulated by multiplying the received signal by the spread code shifted according to the shift amount calculated based on the detection result.

Carrier, high speed synchronization establishment, toggle detection unit, demodulation unit, shift amount, toggle point, received signal

Description

SPECT SPECTRUM SYSTEM COMMUNICATION UNIT AND ITS METHOD FOR ESTABLISHING HIGH SPEED SYNCHRONIZATION

The present invention relates to a spread spectrum communication device, in particular a communication device capable of realizing ultra low power long distance communication, and a high speed synchronization establishment method thereof.

Currently, wireless systems such as wireless LANs and cellular phones are widely used. These radio systems aim to be able to transmit and receive a large amount of information at higher speed, and improvements are being made day by day.

However, in the present society, there are many fields that do not require a great deal of information from one source of information. For example, in the fields of medical systems, meteorological systems, disaster prevention systems, and environmental systems (animal reproduction investigations, alarms, etc.) including wireless nurse calls throughout the hospital, information amount of about 100 bits per minute is often sufficient. . In addition, in the alarm of a situation, the information amount of 1 bit per second may be sufficient.

In such a field, even if the technology related to a wireless LAN, a cellular phone, or the like is applied as it is, practical use is difficult from the viewpoint of power consumption and cost cost. Here, a radio system (ultra low power long distance communication radio system) is required which can overcome power, price cost per communication, and considerable distance. More specifically, for the items, the following performance is required.

Able to realize 50nW output

· Long distance communication (eg 100 m)

Capable of transmitting and receiving information of 1 to 10 bits per second

As described above, since the amount of information transmitted and received is at least irrelevant, the communication speed need not be high speed.

By the way, in order to obtain ultra-high sensitivity in long distance communication, the "identification capability" of the transmission medium (radio wave, sound wave, or light wave) is required, and this "identification capability" is governed by the reception bandwidth. As the reception bandwidth increases, the natural noise power also increases in proportion to this, and the probability of interference with other communications also increases proportionally. Therefore, when the reception bandwidth is made extremely small, the reach distance increases in proportion to this.

In addition, when the reception bandwidth is reduced, the required power can also be reduced. For example, since the general commercial FM (frequency modulation) is about 20 kHz, if it is narrowed down to 1 Hz, the required power becomes 1/2000. One-half of 10mW special small power becomes 0.5mW. Although the 10W amateur radio can communicate with the world, when the reception bandwidth is reduced to 1Hz, the required power is possible at 1/20 of that, 0.5mW.

In this way, by reducing the reception bandwidth (for example, as small as about 1 Hz as described above), there is a possibility that an "ultra low power long distance communication wireless system" corresponding to the above requirements can be realized.

However, the frequency accuracy of the 150MHz crystal oscillator is about 15ppm and the frequency deviation reaches up to 3kHz. This frequency deviation of "3 kHz" is 3000 times different from "1 Hz" in the above example. Therefore, even if the frequency is used every three, it is necessary to find a width of 1000 ch, and it is difficult to exclude the interference of the existing communication simply by reducing the reception bandwidth.

Therefore, consider the application of the spread spectrum communication method to the reception bandwidth is reduced, i.e., "long distance communication with a small occupied bandwidth". If the spread spectrum communication method can be applied within a practical range, interference can be appropriately eliminated without having to search for a carrier wave.

Here, the spread spectrum communication method will be described briefly. This communication method was developed in the field of military and space communication in the 1960s, and is currently used in CDMA (code division multiplexing) of mobile phones, near field communication (Bluetooth) around personal computers, and wireless LAN (Local Area Network). It is widely used.

Originally, spread spectrum communication had two aspects. That is, one side is military and satellite communication in long distance communication with very weak radio waves, and the other side is multiple communication in which a plurality of communication paths are maintained at the same frequency. Currently, the GPS (Global Positioning System) used for car navigation is operated with the emphasis on the long distance communication of the former, and all others operate with the emphasis on the latter multiplexing.

In spread spectrum communication, a spreading code used for modulating (spreading) a carrier wave on a transmitting side is multiplied by a received signal after synchronizing (shifting the spreading code phase by a transmission delay time). By (iii), the original carrier is reproduced on the receiving side. Reproducing the original carrier in this manner is referred to as "despreading" or "demodulation".

In the case of despreading, it is necessary to phase shift the spreading code to be multiplied by the transmission delay time, but in order to successfully receive the transmission delay time without knowing the transmission delay time, the spreading code is slid little by little. The despreading (demodulation) operation is repeatedly executed (for example, the amount of shift to be given to the spreading code is increased by one chip (the minimum time unit of the spreading code) for each execution step), and then reproduced. Depending on whether or not the carrier is at a level level, it is determined whether the reception is successful. This synchronization detection method is called a "slide method." (This synchronization detection method is based on the premise that the frequency of the carrier wave is known on the receiving side.)

According to this synchronization detection method, the time required until the synchronization detection is about M (longest code) sequence cycle time x M series chips, if the M sequence code is used for the spreading code. For example, in a high-speed wireless LAN having a communication speed of 11 MBPS and a spread code length of 11 chips, if the slide method is executed by setting the shift amount to be added per trial step for one chip time, synchronization is performed in 11 attempts at the maximum. Hold. Here, if one chip time is 0.1 microsecond, the time required for one trial is 0.1 microsecond x 11 (chip) = 1.1 microsecond. If 11 attempts are made while sliding this, it is 1.1 microseconds x 11 = 12 microseconds. That is, in such a short time, synchronization for communication is established.

In the GPS having a spread code length of 1023 chips, if synchronous detection is performed while sliding the spread code, at least 1023 chip time (one cycle time of the spread code) is required in one trial, and 50 chips of one chip time are used. If the operation of sliding this in units of% is repeated, synchronization detection succeeds during 2046 slides (i.e., 2046 attempts). That is, the time required until the synchronization detection is 1023 chip time x 2046 = 2 million chip time. If 1 chip time of GPS is 1 microsecond, it will be a maximum of 2 second and an average of 1 second.

Here, in the case where the above-mentioned spread spectrum communication method is applied to the "small occupied bandwidth long distance communication", when the synchronous detection is tested by the slide method, how long will it be? Think about it.

First, when the reception bandwidth is narrowed down to about 1 Hz, it is necessary to set one chip time of a spread code to be used for a certain length (for example, 0.1 m sec = 10 kHz). In the case of using the spread code of 1023 chips, according to the above GPS example, since the longest two million chip time is required for synchronous detection, when one chip time of the spread code is set to 0.1 m sec = 10 kHz, The time required until the synchronization detection is 0.1 m seconds x 2 million (chip time) = 200 seconds. That is, it takes 1 minute and 40 seconds on average and 3 minutes and 20 seconds on the longest until the first 1 bit is detected after the start of reception.

Thus, when spread spectrum communication is applied to long-range communication having a small occupied bandwidth and synchronization detection is tested by the slide method, it takes considerable time. Therefore, unnecessary transmission time for synchronization is required. However, when the transmission time becomes longer, the required power increases by that amount, and the power efficiency per information deteriorates. Therefore, it is difficult to realize "ultra low power long distance communication" by simply applying the spread spectrum communication method to long distance communication with a small occupied bandwidth (first problem).

In addition, when the frequency of the carrier wave is 150 MHz, the wavelength is 2 m. Therefore, when the transmitter starts to move away from the receiver at a speed of 10 m per second or suddenly, the receiver has a frequency less than 5 waves (150 MHz-). 5 Hz), or a carrier wave of five frequencies (150 MHz + 5 Hz). Assuming that the chip time of the spread code is 0.1 m sec and the spread code length is 1023 chip, at this speed, phase change of 0.5 Hz (0.1 m sec x 1023), that is, 180 degrees, during one cycle time (about 0.1 second) Occurs.

In this case, when despreading a received signal and attempting to detect a carrier wave, if the first phase is zero, the phase is reversed on the last side and the synchronization cannot be confirmed (second problem).

In the above example, when the low-speed communication of 1 bit per second (period 1 second) is used, a spread spectrum code of 1023 chips long takes 1023 seconds to establish synchronization, and 20 minutes from the start of reception. If it does not wait, data reception does not start, it takes a very long time, it is not synchronized forever, and there is a problem that it is not practical (third problem).

In addition, as the above improvement, there is a method of digitally processing all of the cycle time to perform synchronous detection. According to this method, it is thought that the synchronization detection time can be shortened. However, when the frequency of the carrier wave cannot be determined with high accuracy, the following problems arise.

If the carrier frequency varies, for example, 150 MHz ± 15 ppm (± 2.25 KHz) (standard Xtal), one chip time of spreading code is 0.1 m second and spread code length is 1023 chip, carrier frequency is 5 Hz If it is misaligned, it is difficult to maintain synchronization, and if it is out of 10 Hz, it can be called another transmission.

That is, in the transmission based on phase modulation, such as spread spectrum communication, the phase amount of a carrier signal is found to be within 0.5 cycles of a carrier over 0.1 second (0.1 m second x 1023) of the spreading code cycle time. If not, the level detection itself of the carrier does not succeed. In other words, in order to establish synchronization of spreading codes, it is necessary to know the frequency of the carrier strictly. To detect carriers in ± 2.25kHz in 10Hz units, 450 trials are required. In other words, when there is a deviation in the frequency of the carrier wave, it is difficult to establish synchronization of the spread code within the practical range (fourth problem).

In the method of digitally detecting all the cycle times and performing synchronous detection, high-speed correlation by surface acoustic wave elements (SAW) or the like is performed as hardware correlation (for example, Japanese Patent Laid-Open No. 9-64787). In order to realize long-distance communication at low communication speed and small power, a physical correlator for a long time is required. However, it is difficult to realize such a correlator (the fifth problem).

In other words, in the conventional method, the frequency and the moving speed of the carrier are known, phase shift can be corrected, and a spread code having a short spread code length is prepared, and a spread code having an appropriate shift amount is prepared. Since detection → synchronization detection is repeated, the phase must be guaranteed over the entire repetition time of the spreading code for synchronization detection. In other words, in order to know the synchronous position of the spread code, the rigor of the frequency of the carrier is required, and if the spread code is not synchronized, the frequency of the carrier cannot be known. That is, in a deadlock state.

The present invention has been made in view of the above problems, and even in a state where ultra low power long distance communication can be realized, synchronization can be established at high speed, and carrier frequencies are not strictly secured, An object of the present invention is to provide a spread spectrum communication device that enables synchronization of spread codes and a synchronization establishment method thereof.

The communication apparatus of the spread spectrum system of the present invention has a toggle detection unit and a demodulation unit, and the toggle detection unit is configured to detect a candidate of the toggle point existing in the received signal carrier, and the demodulation unit is calculated based on the detection result. It is characterized by demodulating the received signal by multiplying the spreading code shifted in accordance with the shift amount to the received signal.

The toggle detection unit is preferably configured to detect a candidate of the toggle point by performing a correlation operation between the expected signal held in advance and the received signal carrier, and the held expected signal is present in the received signal carrier. As a signal containing the waveform of the toggle point which is supposed to be, it is preferable that it is a signal of 2 chip time length of a spreading code, or a signal shorter than that.

The toggle detection unit is further configured to output a toggle signal as a detection result of the toggle point candidate, and based on the cross correlation value between the toggle signal and the absolute value of the derivative value of the spread code, the candidate of the shift amount to be given to the spread code is selected. The demodulation section is configured to perform a demodulation operation on the received signal for each candidate of the shift amount, and the carrier inspection section is configured to check the validity of the carrier spectrum of the received signal demodulated by the demodulation section. desirable.

In addition, when the candidate of the shift amount to be given to the spreading code is calculated, it is preferable that the correlation between the Fourier transform value of the toggle signal and the Fourier transform value of the absolute value of the derivative value of the spreading code is performed.

The fast synchronization establishment method of spread spectrum communication according to the present invention includes a first step of detecting a candidate of a toggle point existing in a received signal carrier wave, a second step of calculating a shift amount based on the detection result, and a calculated The third step of demodulating the received signal is performed in order by multiplying the received signal by the spreading code shifted in accordance with the shift amount.

In this case, as a signal including a waveform of a toggle point that is expected to exist in the reception signal carrier, an expected signal of a length of two chips of a spread code or an expected signal shorter than that is prepared in advance. In one step, it is preferable that a candidate of the toggle point is detected by performing a correlation calculation between the expected signal and the received signal carrier.

In the first step, the toggle signal is output as a detection result of the toggle point candidate, and in the second step, the spread signal should be given to the spread code based on the correlation between the toggle signal and the absolute value of the derivative value of the spread code. It is preferable that the candidates of the shift amounts are calculated, and in the third step, demodulation of the received signals is performed for each candidate of the shift amounts, and the validity of the carrier spectrum of those demodulated signals is checked.

In the second step, when the candidate for the shift amount to be given to the spreading code is calculated, it is preferable that the correlation between the Fourier transform value of the toggle signal and the Fourier transform value of the absolute value of the derivative value of the spread code be performed. .

1 is a block diagram showing a schematic configuration of a receiver in a communication apparatus of the present invention.

FIG. 2 is an explanatory diagram of an expected signal held in the toggle filter 101 shown in FIG. 1.

3 is an explanatory diagram of an example in which the expected signal of FIG. 2 is modified by a window function.

FIG. 4 is an explanatory diagram of "detection of a toggle point candidate" in the toggle filter 101 shown in FIG.

5 is a diagram illustrating a relationship between a received signal, a toggle signal, and a spread code.

FIG. 6 is a diagram showing an example in which a carrier code and a spread code are synchronized as one example of a waveform of a spread code used for spreading a carrier on a transmitting side and a waveform of a carrier spread by a spread code. to be.

7 is a diagram showing an example of waveforms of a carrier wave when the carrier wave and spread code are asynchronous.

8 is a diagram illustrating an example of a received signal when there is noise.

FIG. 9 is a diagram for explaining the relationship between the toggle signal output when the received signal shown in FIG. 8C is input to the toggle filter 101 and the spread code used for spreading the carrier.

FIG. 10 is a diagram showing a result of cross correlation between the toggle signal of FIG. 9 and a spread code. FIG.

11 is a diagram illustrating an example in which a demodulation signal output from the demodulator 105 is detected as a spectrum in the carrier inspection unit 106.

FIG. 12 is a diagram showing another example in which the demodulated signal output from the demodulator 105 is detected as a spectrum in the carrier inspection unit 106. FIG. 12 is a diagram showing an example in which two carriers separated by 10 Hz are mixed and numerically calculated. to be.

(The best mode for carrying out the invention)

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment of this invention is described according to drawing. 1 is a block diagram showing a schematic configuration of a receiver in a communication apparatus of the present invention. As shown in the drawing, the receiver includes a toggle filter (toggle detector) 101, a received signal / toggle signal accumulator 102, a cross-correlator (correlator) 103, a shift amount calculator 104, It consists of elements, such as a demodulator (demodulation part) 105, the carrier test | inspection part 106, and the control part 107. The communication apparatus according to the present invention is a spread spectrum communication apparatus, and communication can be performed under the following conditions.

Carrier frequency: 150 MHz ± 15 ppm (2.25 kHz) (standard Xtal)

Spread code cycle: 1 second

Spread code length: 1023 chips

The signal transmitted and received in this communication apparatus is output from the transmitter side after the carrier wave has been phase-modulated (spread) by a spread code in advance. In this embodiment, this "modulation of a carrier wave by spreading code" is performed by a system called two-phase phase modulation (BPSK). In addition, the modulation method does not necessarily need to be BPSK, but can also be four-phase modulation (QPSK), for example. However, the interference resistance is better in BPSK.

When a signal output from the transmitter side (signal spread by carrier code) is received, the receiver demodulates (despreads) the signal (receive signal), and the original carrier (from the transmitter side) Carrier before spreading) is extracted.

Demodulation is performed by multiplying the received signal by a spreading code (the same code sequence as the spreading code used when spreading the carrier on the transmitter side). At this time, in order to correctly reproduce the original carrier, a large number of toggle points (points and transition points whose phase has been changed by 180 degrees as a result of being modulated by a spreading code) existing in the carrier are to be multiplied for demodulation. Spread code must be synchronized.

Since a phase shift occurs between the signal output from the transmitter side and the received signal due to a transmission delay time and the like, and also due to a frequency deviation, many toggle points exist in the carrier of the received signal. In order to synchronize the spreading code to be multiplied for demodulation, it is necessary to shift the spreading code to the synchronous estimation position. The shift amount required for moving the spread code to the synchronous estimation position is referred to as "α".

Therefore, in the communication apparatus of the present embodiment, first, preliminary detection of the synchronization estimated position (detection of candidates of toggle points existing in the received signal and output of the toggle signal) is performed from the waveform of the received signal (toggle). Filter 101), taking the correlation between the toggle signal and the spreading code (correlator 103), and calculating the candidates α1, α2 ... of the shift amount α based on the correlation value (shift) The amount calculation unit 104 performs despreading for each candidate of the shift amount (demodulator 105), and then examines the extraction state of the carrier to determine whether or not the reception (demodulation) succeeded. (Carrier inspection section 106).

Here, the components constituting the receiver of this communication apparatus and the relationship between the components will be described in detail. First, as shown in FIG. 1, in the receiver of this communication apparatus, the received signal is input to the toggle filter 101 and the received signal / toggle signal accumulator 102. As shown in FIG. Among these, the toggle filter 101 is comprised by the finite impulse response (FIR) digital filter. The toggle filter 101 can also be configured by an IIR (Infinite Impulse Response) digital filter, an accumulator, or the like.

When the received signal is input, the toggle filter 101 detects a candidate (phase change point) of a toggle point existing in the received signal carrier, and forms a toggle signal based on this. In more detail, the toggle filter 101 previously holds the expected signal (or a characteristic calculated from the expected signal) expected by the phase change, and inputs the received signal and the expected signal held in advance. (Or a feature calculated from the expected signal), a correlation operation is performed, a phase change point in the carrier is detected, and a toggle signal is formed and output based on the detected value of the phase change point.

To the output side of the toggle filter 101, a reception signal toggle signal accumulating unit 102 constituted by a memory is connected. That is, the received signal and the toggle signal accumulating unit 102 are input to the toggle signal output from the toggle filter 101 in addition to the received signal as described above. The received received signal and the toggle signal are accumulated as pairs and prepared for post-processing.

The cross-correlator 103 is connected to the toggle signal output side of the received signal / toggle signal accumulation unit 102. This cross-correlator 103 is constituted by cross-correlation means including a DSP (Digital Signal Processor) and a Fourier transformer by hard logic.

The cross-correlator 103 correlates the cross-correlation between the toggle signal (the Fourier transform value of the toggle signal) and the spread code (the Fourier transform value of the absolute value of the differential value of the spread code) output from the received signal / toggle signal accumulation unit 102. And the cross-correlation value S (f) is output.

In more detail, in the cross-correlator 103, the information about the spreading code used for the modulation of the carrier wave is stored in advance in a state processed for convenience for cross-correlation. Processing of the information about the spread code is performed in the following order.

First, the spread code k (t) is differentiated and its absolute value is taken.

d / dtk (t)

d / dtk (t) = ka (t)

This absolute value series ka (t) is Fourier transformed, and this is defined as the conjugate space of cross-correlation.

FFT (ka (t)) → FKA (f)

On the other hand, if the toggle signal input from the received signal / toggle signal accumulator 102 to the cross-correlator 103 is g (t), the cross-correlator 103 uses the toggle signal sequence g (t) as Fourier. Convert.

FFT (g (t)) → G (f)

Next, these values (the Fourier transform value FKA (f) of the absolute value of the derivative value of the spread code) and the Fourier transform value G (f) of the toggle signal sequence are correlated.

S (f) = FKA (f) * G (f)

Then, the obtained result (mutual correlation value S (f)) is output.

The shift amount calculation unit 104 is connected to the output side of the cross-correlator 103. The shift amount calculation unit 104 inversely transforms the cross-correlation value S (f) output from the cross-correlator 103 to s (t). The maximum value of s (t) is regarded as the shift amount α (shift amount necessary to move the spread code to the synchronous estimation position) to be given to the spread code, and the value is large from the value of s (t). In order, a plurality of candidates of the shift amount α are outputted (α 1, α 2...).

Thus, by using Fourier transform instead of the conventional surface acoustic wave element (SAW) or the like, signal processing for a long time is possible.

The demodulator 105 is provided on the reception signal output side of the reception signal / toggle signal accumulation unit 102. The demodulator 105 demodulates the received signal by shifting and multiplying the spread code with respect to the received signal output from the received signal / toggle signal accumulating unit 102.

The shift of the spread code is performed by giving the spread code candidates? 1,? 2, ... of the shift amount output from the shift amount calculation unit 104. More specifically, first, the spreading code is shifted in accordance with the value of the first candidate α1 of the shift amount, and the despreading is carried out by trial. Then, the second candidate α2 and the third candidate of the shift amount are performed. As in (α3), the shift amount candidates are given in sequence to the spread code, and the despreading is repeated every time. Each time such a trial despreading is performed, a demodulated received signal (demodulated signal) is output from the demodulator 105.

The carrier inspection unit 106 is connected to the output side of the demodulator 105. This carrier inspection part 106 is comprised by the Fourier transform unit or a filter. The carrier inspection unit 106 detects the spectrum of each of the plurality of demodulated signals output from the demodulator 105 for each of the candidates α1, α2... Of the shift amount, checks the validity of the carrier spectrum, and confirms synchronization success. The determination is made.

The control unit 107 is connected to the output side of the carrier inspection unit 106. The control unit 107 uses the toggle filter 101, the cross-correlator 103, and the shift amount calculation unit 104 in relation to the above operation based on the result output from the carrier inspection unit 106. To control. In addition, not only the operation | movement as mentioned above but formation of the expected signal in the toggle filter 101, the control of multiple communication etc. which apply and apply a plurality of different spreading codes to the cross-correlator 103, etc. are also this control part. 107.

Next, the specific operation of the receiver shown in FIG. 1 will be described. FIG. 2 is a diagram illustrating an expected signal held in the toggle filter 101 shown in FIG. 1. As described above, the toggle filter 101 detects a candidate of the toggle point existing in the carrier of the received reception signal and outputs a toggle signal. The expected signal shown in the figure is used to detect the candidate of the toggle point. This is a signal pattern for comparison reference (correlation operation).

As shown, the expected signal held in the toggle filter 101 has a toggle point at which the phase is changed by 180 degrees, and the length of one chip time of the spread code (i.e., two chip time) is provided on both sides. This signal is formed by modeling a waveform of a toggle point that is expected to be included in a carrier wave of a received signal as a result of spreading a carrier wave by a spread code, and a partial waveform before and after it.

In this way, the expected signal is set to the length of two chip times of the spreading code so as to be a signal that does not include other toggle points before and after the toggle point located at the center. That is, in the case of such a configuration (or when the length of the expected signal is shorter than two chip times of the spreading code), even if the carrier of the received signal contains a short phase change point due to noise, this is a toggle. The situation where it is detected as a point candidate can be avoided, and only a phase change point appearing at an integer multiple of one chip time can be detected as a toggle point candidate. In addition, the solid line | wire and the dotted line which are shown in FIG. 2 are the real part (cos wave) and the imaginary part (sin wave) of an expected signal, respectively, and are 90 degrees out of phase. These real parts and imaginary parts are used as convenient expressions because they are complexly calculated as a mathematical method of signal processing.

FIG. 3 is a view for explaining an example of deforming the expected signal of FIG. 2 by the window function. 3 (a) is a figure corresponding to FIG. 2, and FIG.3 (b), (c) moves the toggle point of FIG. 3 (a) to the place of 0 (zero), It is a figure which shows the waveform of the expected signal which multiplied and transformed the window function on the whole. In this way, the window function is multiplied by the entirety of the expected signal in order to prepare for the Fourier process to be performed later. In addition, although the front-end part and the rear-end part of the modified expected signal were divided | segmented and shown in FIG.3 (b) and (c), for convenience of explanation here, this modified expected signal is shown in FIG. It is a continuous waveform from the waveform of b) to the waveform of FIG. 3 (c).

In addition, the mask of the window function does not need to be multiplied. In Fig. 3 (a), since the toggle point is at the center of the expected signal, an offset comes out after calculation, in order to set this offset to zero.

4 is a diagram for explaining "detection of a toggle point candidate" in the toggle filter 101 shown in FIG. As shown in Fig. 4A, the expected signal has a waveform in which the phase changes by 180 degrees along the 0 position. In contrast, in the received signal, the waveform portion having the same characteristics as the expected signal (that is, the phase change point of 180 degrees) was present at a position shifted by δ from the 0 position as shown in Fig. 4B. In this case, when a correlation operation is performed between the expected signal of FIG. 4A and the received signal of (B), a correlation result (correlation function) as shown in FIG. 4C is obtained. In the waveform (FIG. 4C) which shows this correlation result, the peak appears in the position (delta) which most likely matches, as shown. The toggle filter 101 outputs a waveform showing this correlation result as a toggle signal.

5 is a diagram illustrating a relationship between a received signal, a toggle signal, and a spread code. The received signal shown in Fig. 5A is a carrier wave (150 MHz ± 15 ppm) that is two-phase modulated by a spread code on the transmitter side. In addition, for the sake of convenience of explanation, it is assumed that noise when passing through the transmission path is not mixed with the received signal.

When the correlation calculation between the received signal shown in Fig. 5A and the expected signal is performed, the correlation result of the waveform as shown by the solid line in Fig. 5B is obtained. The toggle filter 101 outputs the waveform shown by this solid line as a toggle signal.

Among the waveforms of the toggle signal shown in FIG. 5 (b), the peaked portion is the position where the partial waveform of the received signal that most closely matches the waveform of the expected signal is present (that is, a toggle point. Position) is displayed. In fact, when the spreading code (waveform shown by broken line in Fig. 5 (b)) and the toggle signal used to spread the carrier on the transmitting side are superimposed, the peak position in the toggle signal is the phase change of the spreading code. You can see that it matches the point. In this manner, in the receiver of the communication apparatus according to the present embodiment, when a received signal is input, first, a correlation operation between the received signal and the expected signal is performed, so that a candidate of the toggle point included in the received signal is detected. It is.

FIG. 6 is a diagram illustrating an example in which a carrier and a spread code are synchronized as one example of a waveform of a spread code used for spreading a carrier on a transmitting side and a waveform of a carrier spread by a spread code. . 7 is a figure which shows the example of the waveform of a carrier when a carrier and a spreading code are asynchronous.

First, when spread by the spread code shown in Fig. 6A, the carrier becomes a waveform as shown in Fig. 6B. 6 (c) is an enlarged view of a part of the spreading code (part of Q in FIG. 6 (a)) corresponding to a part P of the carrier of FIG. 6 (b), and FIG. 6 (d). Is an enlarged view of a part P of the carrier of FIG. 6 (b).

As shown in Fig. 6 (d), in part P of this carrier, the phase code is changed 180 degrees at the position where the carrier becomes zero by the spread code shown in Fig. 6 (c). In other words, in this example, the spreading code is synchronized at the moment when the carrier crosses zero.

However, when the carrier is spread by the spread code on the transmitting side, the timing at which the spread code is inverted does not necessarily coincide with the moment when the carrier crosses the zero position. In other words, the carrier and the spreading code used for spreading the carrier on the transmitting side are not necessarily synchronized as shown in Fig. 6D.

For example, when the inverted position of the spread code (see FIG. 7 (a)) that spreads the carrier corresponds to the position just before the carrier passes zero and reaches the lower limit, FIG. 7 (b). The waveform includes a toggle point as shown in FIG. In other words, when the carrier is spread on the transmitting side, a toggle point is formed even if the carrier and the spread code are not synchronized.

In the present embodiment, not only when the carrier wave and the spreading code that spreads it are synchronized (see Fig. 6 (d)) but also as shown in Fig. 7 (b), the carrier signal is included in the received signal carrier even when asynchronous. This toggle point can be stably detected (preliminary detection).

This is made possible by the complex calculation in the toggle filter 101. That is, even if a frequency deviation has occurred in the carrier, if the phase of the carrier is guaranteed for at least one chip time (half the length of the expected signal), the toggle filter 101 is not caught by the waveform of the carrier itself. The point where the phase changes 180 degrees (a point considered to be a toggle point) can be detected.

In this way, if the phase of the carrier is guaranteed for at least one chip time, the toggle point can be detected. Therefore, compared with the conventional method (slide method or the like), the phase tolerance is increased by the ratio of the spread code length. In the case of using a spreading code having a period of 1 second and a code length of 1023 chips, there is a tolerance up to a 180 degree change in the carrier phase in two chip times (about 2 m seconds). Therefore, when the carrier frequency is 150 MHz, the tolerance is 250 Hz.

In the case of using a spreading code of a period of 0.1 second and a code length of 1023 chips, there is a tolerance of up to 180 degrees of carrier phase change in about 0.2 m seconds. If the carrier frequency is 150 MHz, the tolerance is 2.5 KHz. In this case, a deviation of ± 16 ppm can be tolerated, so that a normal crystal oscillator can be used, and a very low cost transmission system can be realized.

8 is a diagram illustrating an example of a received signal when there is noise. Fig. 8A is a spreading code used on the transmission side, and Fig. 8B is a transmission signal (150MHz ± 15ppm) in which a carrier wave is two-phase modulated by the spreading code of Fig. 8A. 8 (c) shows a received signal transmitted by the transmission side via the transmission path and received by the receiver.

In the received signal of FIG. 8 (c), a large amount of noise power is applied to the signal power of the transmission signal of FIG. 8 (b), and the S / N ratio (S / N ratio at the band-limited stage in the receiver) It is calculated to be -17.4dＢ.

FIG. 9 is a diagram for explaining the relationship between the toggle signal output when the received signal shown in FIG. 8C is input to the toggle filter 101 and the spread code used for spreading the carrier. In this figure, the waveform shown by the solid line is a toggle signal, and the waveform shown by the broken line is a spread code.

As shown in the figure, when noise is mixed in the received signal, the toggle signal output from the toggle filter 101 is deformed compared with the case where noise is not mixed (see FIG. 5 (b)). . In this toggle signal, the peaked portion indicates the position of the toggle point included in the received signal.

In fact, when the spreading code used for spreading the carrier on the transmitting side and the toggle signal are superimposed, the peak position of the toggle signal is almost coincident with the phase change point of the spreading code. Since the modifying components are mixed, it becomes somewhat difficult to understand.

However, since the step of "outputting the toggle signal by the toggle filter 101" is only preliminary detection of the toggle point, at this point (that is, from the waveform of the toggle signal), the received signal carrier wave The position of the toggle point does not have to be definite. The rigorous investigation of the toggle point, the synchronous estimation position, and the shift amount α is performed based on the toggle signal outputted here (correlation by the cross-correlator 103, the shift amount calculation unit 104). Calculation by the demodulator 105, and spectrum detection by the carrier inspection unit 106).

Fig. 10 shows the cross-correlation of the toggle signal of Fig. 9 (the signal output from the toggle filter 101 as a result of the reception signal of Fig. 8 (c) being input) and the spreading code. It is a figure which shows a result (correlation function). Of the cross-correlation values shown, the maximum value is a candidate (α1, α2 ...) of the shift amount α to be given to the spread code.

In this embodiment, the short time correlation for detection of the toggle point candidate is used to overcome the frequency deviation, perform preprocessing to obtain the toggle signal over the entire spreading code sequence, and then the absolute value of the derivative value of the spreading code and By correlating the toggle signal throughout the spread code sequence and analyzing the result, it is necessary to finally remove the unwanted signal (including multi-power irregular noise) and establish synchronization at high speed. It becomes possible.

11 shows an example in which a demodulation signal output from the demodulator 105 (a received signal demodulated by a spread code shifted by shifting the shift amount α) is detected as a spectrum in the carrier inspection unit 106. FIG. to be. In this example, as shown, one spectrum of 150 MHz can be confirmed.

Thus, according to the present invention, since the frequency deviation of the carrier wave is allowed and even the toggle point where the carrier wave and the spreading code are not synchronized can be stably detected, synchronization can be established at high speed. For this reason, the transmission time and the power for transmission can be made very small. In addition, the shortness of the synchronization capture has a beneficial effect in each aspect, including the problem of incompatibility and battery driving time.

In addition, "high speed" here means specifically, "time for one sequence of spreading codes." That is, synchronization can be established within the time of one sequence of the spreading code used from the start of reception. For example, in the case of using a spreading code having a chip time of 0.1 m second and a code length of 1023 chips, one sequence is 0.1 second.

Therefore, even if eight sequences are transmitted, transmission can be completed in 0.8 seconds and eight bits of information can be sent. For example, if the burst transmission is once every 10 seconds, since only one-twelfth of the time is used, other time can be used for other communication. In addition, spread spectrum communication, which usually requires a long time, is enabled by intermittent communication.

When the carrier frequency is 150 MHz and the spread code length is about 1 second, the frequency deviation of 0.5 Hz can be resolved, and the line speed of 1 m per second from the receiving station can be detected. As a result, the communication quality is improved. It is also possible to communicate with a low quality transmitter attached to an animal (bird, human, etc.) or a slow moving object. Further, the low speed moving body can be used for speed detection and position estimation.

FIG. 12 shows another example in which the demodulated signal output from the demodulator 105 is detected as a spectrum in the carrier inspection unit 106. FIG. 12 shows an example in which two carriers separated by 10 Hz are mixed and numerically calculated. .

As shown, in this example, two spectra, 150 MHz and 150 MHz + 10 Hz, can be identified. In the present invention, since the frequency of the carrier is demodulated and detected after the synchronization is established, information can be transmitted by the frequencies of other carriers having the same spreading code. That is, the deviation of the carrier frequency (150 MHz ± 15 ppm (2.25 kHz)) can be separated by 5 Hz. Therefore, multiple communication is possible.

Moreover, in this embodiment, since it is comprised so that a candidate of a toggle point may be detected first and a spreading code is applied after that, it becomes possible to detect several spreading codes simultaneously. That is, information can be transmitted by using a plurality of spreading codes and a plurality of frequencies of carrier waves. Therefore, multiple communication is possible with a wider method, and therefore, a large amount of communication is possible. Moreover, interference can be suppressed suitably.

In the present embodiment, the toggle filter 101 is used as the toggle detection unit, and the toggle filter 101 is configured to detect the phase change point of the received signal. However, the toggle filter 101 is a toggle filter in a low noise environment. The phase change point of the received signal may be detected by Hilbert transform or by phase detection (phase detection by phase delay or phase locked loop) without using?. In addition, the toggle detection unit may be configured by a surface acoustic wave element (SAW) filter, a DSP, or another circuit.

The present invention is not limited to the transmission medium to be applied, and any one of communication by radio waves, communication by sound waves, and communication by light waves can be suitably applied. In addition, the present invention can be applied to high power spectrum spread communication as well as ultra low power long distance communication.

The spread spectrum communication apparatus of the present invention first detects a candidate of a toggle point existing in a received signal carrier and outputs a toggle signal, and then correlates the output toggle signal with the absolute value of the derivative value of the spread code. The received signal is demodulated by calculating the shift amount of the spread code from the position of the maximum value of cross-correlation and multiplying the spread code shifted according to the calculated shift amount, so that the frequency of the carrier is not strictly known. Even if the spreading code is synchronized, the synchronization can be established.

Therefore, even when a toggle point in which the frequency deviation of the carrier wave is allowed and the carrier signal and the spreading code are not synchronized is included in the received signal, the toggle point can be stably detected, and high-speed synchronization can be realized.

Claims (8)

delete A spread spectrum communication device having a toggle detection unit and a demodulation unit, wherein the toggle detection unit detects a candidate of a toggle point existing in a reception signal carrier by performing a correlation operation between an expected signal held in advance and a reception signal carrier. Wherein the expected signal is a signal including a waveform of a toggle point that is expected to exist in a received signal carrier, and is a signal of a length of two chips of a spread code or a signal shorter than that. The demodulation unit is configured to demodulate the received signal by multiplying the received signal by a spread code shifted according to the shift amount calculated based on the detection result. 3. The toggle detection unit according to claim 2, wherein the toggle detection unit is configured to output a toggle signal as a detection result of the toggle point candidate, and is to be given to the spread code based on a correlation between the toggle signal and the absolute value of the derivative value of the spread code. The candidate of the shift amount is calculated, and the demodulator is configured to demodulate the received signal by shifting the spreading code for each candidate of the shift amount, and is configured to check the validity of the carrier spectrum of the received signal demodulated by the demodulator. Communication device, characterized in that. 4. The method according to claim 3, wherein when the candidate of the shift amount to be given to the spread code is calculated, the correlation between the Fourier transform value of the toggle signal and the Fourier transform value of the absolute value of the derivative value of the spread code is configured. Communication device. delete A first step of detecting a candidate of a toggle point existing in the received signal carrier, a second step of calculating a shift amount based on the detection result, and a spread code shifted according to the calculated shift amount to the received signal By multiplying, the third step of demodulating the received signal is sequentially executed, and includes a waveform of a toggle point that is expected to exist in the received signal carrier, and is a length of two chip times of a spread code. An expected signal of, or a shorter than expected signal is prepared in advance, and in the first step, the candidate of the toggle point is detected by performing a correlation operation between the expected signal and the received signal carrier. Fast synchronization establishment method of spread spectrum communication. 7. The method according to claim 6, wherein in the first step, a toggle signal is output as a detection result of the toggle point candidate, and in the second step, based on a correlation between the toggle signal and the absolute value of the derivative value of the spread code. The candidate of the shift amount to be given to the spreading code is calculated, and in the third step, the received signals are demodulated for each candidate of the shift amount, and the validity of the carrier spectrum of the demodulated received signals is checked. A high-speed synchronization establishment method of spread spectrum communication. 8. The method as claimed in claim 7, wherein in the second step, when the candidate for the shift amount to be given to the spreading code is calculated, the correlation between the Fourier transform value of the toggle signal and the Fourier transform value of the absolute value of the derivative value of the spread code is calculated. A high speed synchronization establishment method of spread spectrum communication, characterized in that performed.

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